1. Field of the Invention
The present invention generally relates to a resonance-frequency measuring method used for an information recording and/or reproducing device, an information recording and/or reproducing device, and an electric filter, and, more particularly, to a resonance-frequency measuring method for measuring a resonance frequency of a mechanism unit of an information recording and/or reproducing device driven by the mechanism unit to record and/or reproduce information, an information recording and/or reproducing device, and an electric filter.
An information recording and/or reproducing device, such as a hard disk drive, is required to record and/or reproduce information at a high speed with a high recording density. These requirements raise a problem of head vibration due to a resonance of a mechanism unit. In order to repress a resonance component of the mechanism unit, such an information recording and/or reproducing device incorporates a notch filter for removing a resonance component from a head-driving signal. Since mechanism units of different devices have different resonance frequencies, a cutoff frequency of the notch filter needs to be set individually by measuring a resonance frequency for each different device. Therefore, an efficient method for measuring a resonance frequency has been desired.
2. Description of the Related Art
First, a description will be given, with reference to the drawings, of a hard disk drive.
FIG. 1A is a cross-sectional view of a structure of a hard disk drive. FIG. 1B is a plan view of the structure of the hard disk drive. FIG. 2 is a block diagram of the hard disk drive.
A hard disk drive 1 mainly comprises a disk enclosure 11 and a circuit assembly 12. The disk enclosure 11 contains a magnetic disk 21, a spindle motor 22, a magnetic head 23, a head arm 24, a voice coil motor 25 (a mechanism unit), and a head IC (Integrated Circuit) 26. The magnetic disk 21 is fixed to a rotating shaft of the spindle motor 22, and revolves in accordance with the rotation of the spindle motor 22.
The magnetic head 23 is arranged opposite the magnetic disk 21, and acts magnetically on the magnetic disk 21 so as to record and/or reproduce information. The magnetic head 23 is fixed on an end of the head arm 24. The head arm 24 is coupled with the voice coil motor 25 at the other end so as to be revolved by the voice coil motor 25. Along with the revolution of the head arm 24, the magnetic head 23 moves in a radial direction of the magnetic disk 21.
The magnetic head 23 is connected to the head IC 26. The head IC 26 amplifies a signal that is to be recorded on the magnetic disk 21 by the magnetic head 23, and supplies the amplified signal to the magnetic head 23. The head IC 26 also amplifies a reproduction signal that is reproduced from the magnetic disk 21 by the magnetic head 23, and supplies the amplified reproduction signal to the circuit assembly 12.
As shown in FIG. 2, the circuit assembly 12 includes a read channel (RDC) 31, an MPU (Micro Processing Unit) 32, a ROM (Read Only Memory) 33, a servo controller (SVC) 34 (an actuator; a driving unit), a hard disk controller (HDC) 35, a RAM (Random Access Memory) 36, and an IDE (Integrated Device Electronics) connector 37.
The read channel 31 is connected with the head IC 26. The read channel 31 supplies a record signal to the head IC 26, and also demodulates a reproduction signal amplified by the head IC 26 into reproduction data. The reproduction data demodulated by the read channel 31 is supplied to the HDC 35. The HDC 35 temporarily stores the reproduction data in the RAM 36, and thereafter, supplies the reproduction data to a host computer (not shown in the figure) via the IDE connector 37.
Record data is supplied from the host computer to the IDE connector 37. The HDC 35 temporarily stores the record data in the RAM 36. Upon recording, the HDC 35 reads the record data from the RAM 36, and supplies the record data to the read channel 31. The read channel 31 modulates the record data so as to generate a record signal. The record signal generated by the read channel 31 is supplied to the head IC 26. The head IC 26 amplifies the record signal, and supplies the amplified record signal to the magnetic head 23. The magnetic head 23 magnetizes the magnetic disk 21 by producing a magnetic field corresponding to the record signal so as to record the record signal on the magnetic disk 21.
In the above-mentioned course, the MPU 32 is supplied with the reproduction data demodulated by the read channel 31. The MPU 32 reads a location signal (a present location signal) indicating an address on the magnetic disk 21 from the reproduction data, and performs a tracking servo control. The MPU 32 generates a control signal, i.e., a tracking error signal, corresponding to a difference between the read location signal and a location signal (an aimed location signal) representing a location where aimed information is recorded, and performs a notch-filter process to the generated control signal. Thereafter, the MPU 32 supplies the control signal to the servo controller 34. The notch-filter process removes a device's natural resonance frequency component from the control signal.
The servo controller 34 controls the voice coil motor 25 according to the control signal supplied from the MPU 32 so as to regulate a reading position of the magnetic head 23 reading a signal from the magnetic disk 21.
Thus, the magnetic head 23 can scan the aimed location on the magnetic disk 21 so as to obtain the aimed information.
In this course, the voice coil motor 25 exhibits a device-specific resonance frequency. Therefore, a firmware executed by the MPU 32 includes a resonance-frequency measuring process for measuring the device-specific resonance frequency so as to match a cutoff frequency in the notch-filter process to the device-specific resonance frequency.
FIG. 3 is a functional block diagram of a conventional example of a tracking servo control system.
It is noted that a subtracter 41, a controller 42, a notch filter 43, an adder 44, a sine-wave disturbance generator 45, an FFT calculator 46, and an adjuster 47 are realized by the firmware as processes of the MPU 32.
The subtracter 41 is supplied with the aimed location signal and the present location signal, and calculates the difference between the aimed location signal and the present location signal so as to output difference information. The difference information is supplied to the controller 42. Based on the difference information supplied from the subtracter 41, the controller 42 generates the control signal for controlling the voice coil motor 25.
The control signal generated by the controller 42 is supplied to the notch filter 43. The notch filter 43 deducts a preset cutoff frequency component from the control signal. The control signal without the unnecessary component is supplied from the notch filter 43 to the adder 44. The adder 44 adds a sine-wave disturbance signal supplied from the sine-wave disturbance generator 45 to the control signal supplied from the notch filter 43. The control signal including the sine-wave disturbance signal is supplied to the servo controller 34.
Based on the control signal supplied from the adder 44, the servo controller 34 generates a driving signal for driving the voice coil motor 25. The driving signal generated by the servo controller 34 is supplied to the voice coil motor 25. The voice coil motor 25 is driven by the driving signal supplied from the servo controller 34 so as to alter a position of the magnetic head 23.
The magnetic head 23 reads a signal from the magnetic disk 21 at the altered position. This reproduction signal reproduced by the magnetic head 23 is supplied to the head IC 26. The head IC 26 amplifies the reproduction signal supplied from the magnetic head 23. The reproduction signal amplified by the head IC 26 is supplied to the read channel 31. The read channel 31 demodulates the reproduction signal so as to obtain reproduction information. A location signal included in the reproduction information is supplied, as the present location signal, to the subtracter 41 and the FFT (Fast Fourier Transform) calculator 46. The FFT calculator 46 performs an FFT process so as to calculate amplitude of the location signal.
The amplitude of the location signal calculated in the FFT calculator 46 is supplied to the adjuster 47. The adjuster 47 detects a frequency of the sine-wave disturbance signal generated by the sine-wave disturbance generator 45 that maximizes the calculation result, i.e., the amplitude of the location signal, of the FFT calculator 46 by varying the frequency of the sine-wave disturbance signal and obtaining the calculation result of the FFT calculator 46. The adjuster 47 sets the detected maximizing frequency as the cutoff frequency in the notch filter 43.
Besides, in order to calculate the amplitude of the location signal, a DFT (Discrete. Fourier Transform Analysis) calculator and a Max-Min difference calculator are generally used in addition to the FFT calculator 46.
In measuring the resonance frequency in the conventional hard disk drive, the resonance frequency is calculated by the FFT calculator 46, the DFT calculator and the Max-Min difference calculator. However, there have been problems, such as that the FFT calculation, the DFT calculation and the Max-Min difference calculation are so complicated, and require large memory usage.